1. Field of the Invention
The present invention relates, in general, to a device for etching the backside of a wafer and, more particularly, to a device for chemically etching the backside of a thin wafer before a vapor-deposition process of depositing a metal layer on the backside of the wafer.
2. Description of the Prior Art
In a conventional process of producing semiconductor devices, such as diodes or transistors, the backside of a target wafer after a wafer fabrication process is initially ground until the wafer is thinned to a desired level. After the grinding process, the backside of the wafer is etched prior to being layered with a metal layer through a vapor-deposition process. The etching process for the backside of the wafer is to reduce the contact resistance between the wafer material, such as Si, and the metal of the layer formed on the backside of the wafer through the vapor-deposition process.
During such an etching process of chemically cutting the backside of the wafer, it is necessary to protect the metallizations arrayed on the front side of the wafer from any damage. In order to protect such metallizations during the etching process, an absorption fabric has been used in the prior art. The etching process using such an absorption fabric has been called xe2x80x9can etching process using an absorption fabricxe2x80x9d. In such an etching process using an absorption fabric, the absorption fabric is sufficiently drenched in an etchant before the absorption fabric comes into surface contact with only the backside of a target wafer so as to etch only the backside.
FIG. 1A is a perspective view of a conventional device for etching the backside of a wafer through an etching process using an absorption fabric. During an etching process using the device, an etchant is fed from an etchant supply source (not shown) into an etching bath 12, with an absorption fabric 14 immersed in the etchant to sufficiently absorb the etchant as shown in the drawing. Thereafter, a wafer 16 is laid on the absorption fabric 14 such that the backside of the wafer 16 is etched by the etchant of the fabric 14. After the backside of the wafer 16 is etched to a desired level, the wafer 16 is removed from the fabric 14, thus finishing the process of etching the backside of the wafer 16.
However, the conventional etching process using an absorption fabric is problematic in that the wafer may be easily damaged during the process. Such a problem of damaging the wafer is typically caused when the wafer 16 is removed from the absorption fabric 14 as shown in FIG. 1B. That is, the removal of the wafer 16 from the fabric 14 is carried out by using tweezers 18. However, when the wafer 16 is removed from the fabric 14 using the tweezers 18 as shown in FIG. 1B, surface tension caused by the etchant is generated at the junction xe2x80x9cAxe2x80x9d of the wafer 16 and the fabric 14. Due to the surface tension produced at the junction xe2x80x9cAxe2x80x9d during the removal of the wafer from the fabric 14, stress is applied to the wafer 16 in a direction opposite to the wafer separation force applying direction, thus easily damaging or breaking the wafer 16. In recent years, the wafers have been enlarged and reduced in their thickness to a level of no thicker than 200 xcexcm, and so the thin wafers may be more easily damaged or broken during such a process of removing a wafer from an absorption fabric after an etching process.
When the backside of a target wafer is etched through the conventional etching process using an absorption fabric, the wafer may fail to come into uniform contact at its backside with the absorption fabric. In such a case, it is very difficult to uniformly etch the backside of the wafer. Reaction debris produced during the etching process is typically accumulated at a position around the backside of the wafer, and so it is almost impossible to accomplish the desired etching effect for the backside of the wafer.
In addition, it is very difficult to appropriately control the temperature of the etchant during the removal of the wafer from the absorption fabric since the fabric is sufficiently drenched with the etchant.
In a conventional process of etching the backside of a wafer using an absorption fabric, the etching effect is accomplished by the absorption fabric sufficiently drenched in the etchant. However, since the etching process is carried out by the absorption fabric coming into contact with the backside of the wafer, the wafer may be severely damaged due to the surface tension caused by the etchant when the wafer is removed from the absorption fabric. In addition, due to both the nonuniform contact between the wafer and the absorption fabric and the reaction debris typically accumulated at a position around the backside of the wafer during an etching process, it is almost impossible for the conventional etching process using the absorption fabric to accomplish uniform etching effect.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art and an object of the present invention is to provide a device for etching the backside of a wafer, which directly feeds an etchant to a target wafer without using any medium, such as a conventional absorption fabric, thus uniformly etching the backside of the wafer, and which prevents the wafer from coming into contact with the etchant during the removal of the wafer from the etching device, thus almost completely protecting the wafer from any damage.
Another object of the present invention is to provide a wafer etching system, which includes the above etching device designed to protect the wafer from any damage during an etching process, and which uniformly etches the backside of the wafer while easily controlling the temperature of the etchant as desired during the etching process.
In order to accomplish the above object, the present invention provides a device for etching the backside of a wafer, comprising: a cylindrical housing having a bottom wall, the bottom wall being conically shaped such that the bottom wall peaks at its center; an annular etching dam seated on the upper surface of the conical bottom wall of the housing, with an etchant collecting chamber defined between the sidewall of the dam and the sidewall of the housing, and an etching bath defined inside the dam for containing an etchant; an etchant supply unit provided on the conical bottom wall of the housing for feeding the etchant into the etching bath; and at least one first etchant discharging part formed at the junction of the etching dam and the housing, and allowing the etching bath to communicate with the etchant collecting chamber, and at least one second etchant discharging part formed on the lower portion of the sidewall of the housing, and allowing the etchant collecting chamber to communicate with the outside of the device, whereby the target wafer is seated on the upper portion of the etching dam, and is etched at its backside by the etchant fed from the etchant supply unit into the etching bath.
In an embodiment, a plurality of wafer support pieces are provided along the top edge of the etching dam for supporting the wafer, and allow the etchant from the etching bath to flow over the top edge of the dam to reach the etchant collecting chamber through a plurality of spaces defined between the wafer support pieces and the top edge of the dam.
In another embodiment, the etching dam is inclined at its top edge downward toward the etchant collecting chamber. In addition, at least one hole is formed at the upper portion of the sidewall of the dam, thus forming a third etchant discharging part communicating the etching bath with the etchant collecting chamber.
In the etching device, the etching dam consists of an annular body, formed by the sidewall integrated with inclined upper and lower walls, the upper wall extending from the top edge of the sidewall of the dam while being inclined downward in a direction toward the center of the dam, and the lower wall extending from the bottom edge of the sidewall while being inclined upward in a direction toward the center of the dam, with an inclination angle of the lower wall being the same as that of the conical bottom wall of the housing.
The present invention also provides an etching system, comprising: an etchant storage tank, a pump, and a flow controller, in addition to the above-mentioned etching device.